Milling cutters may be equipped with a plurality of small and round cutting inserts that are generally pulley-shaped and have a circular, endless edge between a topside and a circumferential clearance surface, as well as a number of out of round engagement surfaces adjacent to the underside. A usual existing cutting insert of this type is formed with six planar, identical and equidistant engagement surfaces, which together give the bottom part of the cutting insert a hexagonal, nut-like shape. By bringing this bottom part in engagement with a mating, hexagonal countersink in the bottom of the insert seat, the cutting insert is rotationally secured, i.e., is kept in position without rotating. Simultaneously, the cutting forces, which are considerably greater than the forces that aim to rotate the cutting insert, are carried by the bottom of the insert seat, as well as by one or more rotationally symmetrical arched side support surfaces against which the rotationally symmetrical and endless clearance surface of the cutting insert is pressed.
As long as the cutting inserts are large and few in number, the polygonal countersink in the bottom of the individual insert seat can be made without major difficulties, viz. by milling and/or drilling by means of conventional cutting tools. However, if the milling cutter should be equipped with small cutting inserts, and in particular, many small cutting inserts, difficulties arise in forming the countersink. In such cases, the plurality of (e.g., six) planar shoulder surfaces, which together form the countersink, will become so exceptionally small that traditional cutting tools cannot be used to generate the proper surfaces, as well as the requisite clearances between the same. Studies made on the question whether it would be possible to mill cut the surfaces by means of special shank-end mills having a diameter of down to 1 mm have shown that this alternative is not realistic. When the insert seats are numerous, i.e., located close to each other, the accessibility for the cutting tools is further reduced.
The present invention aims at obviating the above-mentioned difficulties. Therefore, a primary object of the invention is to provide a tool that can be constructed with small and numerous cutting inserts, which are rotationally secured by the use of means that are simple and inexpensive to provide.
Another object of the invention is to improve the rotational securing of the cutting inserts so far that the risk of unintentional rotation of the cutting insert is minimized.
Yet another object of the invention is to provide a tool in which the risk of damage, e.g., wear damage, to the expensive basic body is reduced to a minimum.